The invention belongs to the field of resource recycling and building materials and discloses a steam curing method of baking-free manganese slag bricks. The steam curing method comprises steps as follows: the baking-free manganese slag bricks are placed in a steam curing reaction tank, and steam curing is performed in three stages including a temperature increase stage, a constant temperature stage and a temperature decrease stage; the temperature increase stage is sequentially divided into three stages: the temperature is increased to 60-70 DEG C in the first stage and kept for 10-15 min, the temperature is increased to 80-85 DEG C in the second stage and kept for 20-30 min, the temperature is increased to 100-110 DEG C in the third stage, and then the constant temperature stage begins. The curing method solves problems that bodies of the baking-free bricks have faults and inner holes, the bodies are half-baked, the bricks crack, edges fall off, the strength is low, the durability is poor and the like, requirements for curing equipment are low, operation is simple and convenient, and the production cost is low.